1. Field of the Invention
The invention relates to data storage technology, and in particular, to data storage devices utilizing liquid bearing materials at the interface between storage media and a data recording head, to methods of writing and reading data using such liquid bearing materials and to the bearing materials themselves.
2. Description of the Related Art
In most conventional disk drives, a read/write head moves over an air cushion or "bearing" that supports the head above a magnetic recording disk surface. Other drives, as described, for example, in European Patent Application No. 0367510 and U.S. Pat. No. 5,097,368, use liquids such as hydrocarbons, in particular normal hexadecane, and fluorinated compounds, such as polyfluoropolyether (PFPE), respectively, as liquid bearing materials at the head-disk interface.
A number of problems have been associated with such conventional liquid bearing materials. Some liquid bearing materials can evaporate readily from the disk surface and from within the drive housing to the ambient surroundings. Also, drive operating and/or storage conditions may be relatively too cold so that conventional liquid bearing materials, such as hydrocarbons including n-hexadecane, freeze and therefore cannot function as desired. Likewise, many hydrocarbon liquids are inappropriate as liquid bearing materials because of their tendency to oxidize. In addition, some materials, such as some esters and ketones may insufficiently wet the disk surface because of undesirably high surface tension. Other materials, such as PFPE, are difficult to transport within the drive because of inadequate surface tension. Also, some materials may be too viscous or may be incompatible with so-called disk lubricants applied during standard thin film disk manufacturing techniques to be useful liquid bearing materials for the head-disk interface.
Other problems can occur where the liquid bearing material is also used as a drive lubricant, i.e., where the liquid bearing/lubricant is cycled, as by wicking, between the head-disk interface and the drive elements. For instance, some liquid bearing materials act as solvents with respect to drive elements such as adhesives and plastics, thereby having deleterious effects on the drive. In particular, some substances can be dissolved from these elements and over time can oxidize or otherwise breakdown because of the severe temperature, pressure and shear conditions at the head-disk interface. Deposits can form thereby on the head, forcing the head away from the disk and impeding accurate information transfer between the head and the disk.
Antioxidants are commonly used in rubbers, petroleum-based products, adhesives and foods for retarding oxidation by atmospheric oxygen. Antiwear agents, such as boundary layer lubricants, can further reduce friction and wear by forming surface films known to adsorb chemically or physically onto the surfaces to be lubricated. While these are commonly used additives in other technologies, the disk drive industry has not utilized such in conjunction with conventional liquid bearing materials at the head-disk interface.
Mere incorporation of additives may be insufficient in and of itself to make a serviceable liquid bearing material. For example, PFPE exhibits sufficient oxidative stability to obviate need for antioxidant additives, but has inadequate surface tension to wick, impeding its circulation within a disk drive. Moreover, for other potential liquid bearing materials, any enhancement to long-term stability might be achieved at the expense of lubricative properties, drive and/or head performance, especially in terms of the accuracy of information transfer.